/******************************************************
Row versions

(c) 1997 Innobase Oy

Created 2/6/1997 Heikki Tuuri
*******************************************************/

#include "row0vers.h"

#ifdef UNIV_NONINL
#include "row0vers.ic"
#endif

#include "dict0dict.h"
#include "dict0boot.h"
#include "btr0btr.h"
#include "mach0data.h"
#include "trx0rseg.h"
#include "trx0trx.h"
#include "trx0roll.h"
#include "trx0undo.h"
#include "trx0purge.h"
#include "trx0rec.h"
#include "que0que.h"
#include "row0row.h"
#include "row0upd.h"
#include "rem0cmp.h"
#include "read0read.h"
#include "lock0lock.h"

/*********************************************************************
Finds out if an active transaction has inserted or modified a secondary
index record. NOTE: the kernel mutex is temporarily released in this
function! */

trx_t *row_vers_impl_x_locked_off_kernel(
    /*==============================*/
    /* out: NULL if committed, else the active
    transaction; NOTE that the kernel mutex is
    temporarily released! */
    rec_t *rec,           /* in: record in a secondary index */
    dict_index_t *index,  /* in: the secondary index */
    const ulint *offsets) /* in: rec_get_offsets(rec, index) */
{
  dict_index_t *clust_index;
  rec_t *clust_rec;
  ulint *clust_offsets;
  rec_t *version;
  rec_t *prev_version;
  dulint trx_id;
  dulint prev_trx_id;
  mem_heap_t *heap;
  mem_heap_t *heap2;
  dtuple_t *row;
  dtuple_t *entry = NULL; /* assignment to eliminate compiler
                          warning */
  trx_t *trx;
  ulint vers_del;
  ulint rec_del;
  ulint err;
  mtr_t mtr;
  ulint comp;

#ifdef UNIV_SYNC_DEBUG
  ut_ad(mutex_own(&kernel_mutex));
  ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));
#endif /* UNIV_SYNC_DEBUG */

  mutex_exit(&kernel_mutex);

  mtr_start(&mtr);

  /* Search for the clustered index record: this is a time-consuming
  operation: therefore we release the kernel mutex; also, the release
  is required by the latching order convention. The latch on the
  clustered index locks the top of the stack of versions. We also
  reserve purge_latch to lock the bottom of the version stack. */

  clust_rec = row_get_clust_rec(BTR_SEARCH_LEAF, rec, index, &clust_index, &mtr);
  if (!clust_rec)
  {
    /* In a rare case it is possible that no clust rec is found
    for a secondary index record: if in row0umod.c
    row_undo_mod_remove_clust_low() we have already removed the
    clust rec, while purge is still cleaning and removing
    secondary index records associated with earlier versions of
    the clustered index record. In that case there cannot be
    any implicit lock on the secondary index record, because
    an active transaction which has modified the secondary index
    record has also modified the clustered index record. And in
    a rollback we always undo the modifications to secondary index
    records before the clustered index record. */

    mutex_enter(&kernel_mutex);
    mtr_commit(&mtr);

    return (NULL);
  }

  heap = mem_heap_create(1024);
  clust_offsets = rec_get_offsets(clust_rec, clust_index, NULL, ULINT_UNDEFINED, &heap);
  trx_id = row_get_rec_trx_id(clust_rec, clust_index, clust_offsets);

  mtr_s_lock(&(purge_sys->latch), &mtr);

  mutex_enter(&kernel_mutex);

  trx = NULL;
  if (!trx_is_active(trx_id))
  {
    /* The transaction that modified or inserted clust_rec is no
    longer active: no implicit lock on rec */
    goto exit_func;
  }

  if (!lock_check_trx_id_sanity(trx_id, clust_rec, clust_index, clust_offsets, TRUE))
  {
    /* Corruption noticed: try to avoid a crash by returning */
    goto exit_func;
  }

  comp = page_rec_is_comp(rec);
  ut_ad(index->table == clust_index->table);
  ut_ad(!!comp == index->table->comp);
  ut_ad(!comp == !page_rec_is_comp(clust_rec));

  /* We look up if some earlier version, which was modified by the trx_id
  transaction, of the clustered index record would require rec to be in
  a different state (delete marked or unmarked, or have different field
  values, or not existing). If there is such a version, then rec was
  modified by the trx_id transaction, and it has an implicit x-lock on
  rec. Note that if clust_rec itself would require rec to be in a
  different state, then the trx_id transaction has not yet had time to
  modify rec, and does not necessarily have an implicit x-lock on rec. */

  rec_del = rec_get_deleted_flag(rec, comp);
  trx = NULL;

  version = clust_rec;

  for (;;)
  {
    mutex_exit(&kernel_mutex);

    /* While we retrieve an earlier version of clust_rec, we
    release the kernel mutex, because it may take time to access
    the disk. After the release, we have to check if the trx_id
    transaction is still active. We keep the semaphore in mtr on
    the clust_rec page, so that no other transaction can update
    it and get an implicit x-lock on rec. */

    heap2 = heap;
    heap = mem_heap_create(1024);
    err = trx_undo_prev_version_build(clust_rec, &mtr, version, clust_index, clust_offsets, heap, &prev_version);
    mem_heap_free(heap2); /* free version and clust_offsets */

    if (prev_version)
    {
      clust_offsets = rec_get_offsets(prev_version, clust_index, NULL, ULINT_UNDEFINED, &heap);
      row = row_build(ROW_COPY_POINTERS, clust_index, prev_version, clust_offsets, heap);
      entry = row_build_index_entry(row, index, heap);
    }

    mutex_enter(&kernel_mutex);

    if (!trx_is_active(trx_id))
    {
      /* Transaction no longer active: no implicit x-lock */

      break;
    }

    /* If the transaction is still active, the previous version
    of clust_rec must be accessible if not a fresh insert; we
    may assert the following: */

    ut_ad(err == DB_SUCCESS);

    if (prev_version == NULL)
    {
      /* It was a freshly inserted version: there is an
      implicit x-lock on rec */

      trx = trx_get_on_id(trx_id);

      break;
    }

    /* If we get here, we know that the trx_id transaction is
    still active and it has modified prev_version. Let us check
    if prev_version would require rec to be in a different
    state. */

    vers_del = rec_get_deleted_flag(prev_version, comp);

    /* We check if entry and rec are identified in the alphabetical
    ordering */
    if (0 == cmp_dtuple_rec(entry, rec, offsets))
    {
      /* The delete marks of rec and prev_version should be
      equal for rec to be in the state required by
      prev_version */

      if (rec_del != vers_del)
      {
        trx = trx_get_on_id(trx_id);

        break;
      }

      /* It is possible that the row was updated so that the
      secondary index record remained the same in
      alphabetical ordering, but the field values changed
      still. For example, 'abc' -> 'ABC'. Check also that. */

      dtuple_set_types_binary(entry, dtuple_get_n_fields(entry));
      if (0 != cmp_dtuple_rec(entry, rec, offsets))
      {
        trx = trx_get_on_id(trx_id);

        break;
      }
    }
    else if (!rec_del)
    {
      /* The delete mark should be set in rec for it to be
      in the state required by prev_version */

      trx = trx_get_on_id(trx_id);

      break;
    }

    prev_trx_id = row_get_rec_trx_id(prev_version, clust_index, clust_offsets);

    if (0 != ut_dulint_cmp(trx_id, prev_trx_id))
    {
      /* The versions modified by the trx_id transaction end
      to prev_version: no implicit x-lock */

      break;
    }

    version = prev_version;
  } /* for (;;) */

exit_func:
  mtr_commit(&mtr);
  mem_heap_free(heap);

  return (trx);
}

/*********************************************************************
Finds out if we must preserve a delete marked earlier version of a clustered
index record, because it is >= the purge view. */

ibool row_vers_must_preserve_del_marked(
    /*==============================*/
    /* out: TRUE if earlier version should be preserved */
    dulint trx_id, /* in: transaction id in the version */
    mtr_t *mtr)    /* in: mtr holding the latch on the clustered index
                   record; it will also hold the latch on purge_view */
{
#ifdef UNIV_SYNC_DEBUG
  ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));
#endif /* UNIV_SYNC_DEBUG */

  mtr_s_lock(&(purge_sys->latch), mtr);

  if (trx_purge_update_undo_must_exist(trx_id))
  {
    /* A purge operation is not yet allowed to remove this
    delete marked record */

    return (TRUE);
  }

  return (FALSE);
}

/*********************************************************************
Finds out if a version of the record, where the version >= the current
purge view, should have ientry as its secondary index entry. We check
if there is any not delete marked version of the record where the trx
id >= purge view, and the secondary index entry and ientry are identified in
the alphabetical ordering; exactly in this case we return TRUE. */

ibool row_vers_old_has_index_entry(
    /*=========================*/
    /* out: TRUE if earlier version should have */
    ibool also_curr,     /* in: TRUE if also rec is included in the
                       versions to search; otherwise only versions
                       prior to it are searched */
    rec_t *rec,          /* in: record in the clustered index; the
                         caller must have a latch on the page */
    mtr_t *mtr,          /* in: mtr holding the latch on rec; it will
                         also hold the latch on purge_view */
    dict_index_t *index, /* in: the secondary index */
    dtuple_t *ientry)    /* in: the secondary index entry */
{
  rec_t *version;
  rec_t *prev_version;
  dict_index_t *clust_index;
  ulint *clust_offsets;
  mem_heap_t *heap;
  mem_heap_t *heap2;
  dtuple_t *row;
  dtuple_t *entry;
  ulint err;
  ulint comp;

  ut_ad(mtr_memo_contains(mtr, buf_block_align(rec), MTR_MEMO_PAGE_X_FIX) ||
        mtr_memo_contains(mtr, buf_block_align(rec), MTR_MEMO_PAGE_S_FIX));
#ifdef UNIV_SYNC_DEBUG
  ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));
#endif /* UNIV_SYNC_DEBUG */
  mtr_s_lock(&(purge_sys->latch), mtr);

  clust_index = dict_table_get_first_index(index->table);

  comp = page_rec_is_comp(rec);
  ut_ad(!index->table->comp == !comp);
  heap = mem_heap_create(1024);
  clust_offsets = rec_get_offsets(rec, clust_index, NULL, ULINT_UNDEFINED, &heap);

  if (also_curr && !rec_get_deleted_flag(rec, comp))
  {
    row = row_build(ROW_COPY_POINTERS, clust_index, rec, clust_offsets, heap);
    entry = row_build_index_entry(row, index, heap);

    /* NOTE that we cannot do the comparison as binary
    fields because the row is maybe being modified so that
    the clustered index record has already been updated
    to a different binary value in a char field, but the
    collation identifies the old and new value anyway! */

    if (dtuple_datas_are_ordering_equal(ientry, entry))
    {
      mem_heap_free(heap);

      return (TRUE);
    }
  }

  version = rec;

  for (;;)
  {
    heap2 = heap;
    heap = mem_heap_create(1024);
    err = trx_undo_prev_version_build(rec, mtr, version, clust_index, clust_offsets, heap, &prev_version);
    mem_heap_free(heap2); /* free version and clust_offsets */

    if (err != DB_SUCCESS || !prev_version)
    {
      /* Versions end here */

      mem_heap_free(heap);

      return (FALSE);
    }

    clust_offsets = rec_get_offsets(prev_version, clust_index, NULL, ULINT_UNDEFINED, &heap);

    if (!rec_get_deleted_flag(prev_version, comp))
    {
      row = row_build(ROW_COPY_POINTERS, clust_index, prev_version, clust_offsets, heap);
      entry = row_build_index_entry(row, index, heap);

      /* NOTE that we cannot do the comparison as binary
      fields because maybe the secondary index record has
      already been updated to a different binary value in
      a char field, but the collation identifies the old
      and new value anyway! */

      if (dtuple_datas_are_ordering_equal(ientry, entry))
      {
        mem_heap_free(heap);

        return (TRUE);
      }
    }

    version = prev_version;
  }
}

/*********************************************************************
Constructs the version of a clustered index record which a consistent
read should see. We assume that the trx id stored in rec is such that
the consistent read should not see rec in its present version. */

ulint row_vers_build_for_consistent_read(
    /*===============================*/
    /* out: DB_SUCCESS or DB_MISSING_HISTORY */
    rec_t *rec,               /* in: record in a clustered index; the
                              caller must have a latch on the page; this
                              latch locks the top of the stack of versions
                              of this records */
    mtr_t *mtr,               /* in: mtr holding the latch on rec */
    dict_index_t *index,      /* in: the clustered index */
    ulint **offsets,          /* in/out: offsets returned by
                              rec_get_offsets(rec, index) */
    read_view_t *view,        /* in: the consistent read view */
    mem_heap_t **offset_heap, /* in/out: memory heap from which
                          the offsets are allocated */
    mem_heap_t *in_heap,      /* in: memory heap from which the memory for
                              old_vers is allocated; memory for possible
                              intermediate versions is allocated and freed
                              locally within the function */
    rec_t **old_vers)         /* out, own: old version, or NULL if the
                             record does not exist in the view, that is,
                             it was freshly inserted afterwards */
{
  rec_t *version;
  rec_t *prev_version;
  dulint prev_trx_id;
  mem_heap_t *heap = NULL;
  byte *buf;
  ulint err;

  ut_ad(index->type & DICT_CLUSTERED);
  ut_ad(mtr_memo_contains(mtr, buf_block_align(rec), MTR_MEMO_PAGE_X_FIX) ||
        mtr_memo_contains(mtr, buf_block_align(rec), MTR_MEMO_PAGE_S_FIX));
#ifdef UNIV_SYNC_DEBUG
  ut_ad(!rw_lock_own(&(purge_sys->latch), RW_LOCK_SHARED));
#endif /* UNIV_SYNC_DEBUG */

  ut_ad(rec_offs_validate(rec, index, *offsets));

  ut_ad(!read_view_sees_trx_id(view, row_get_rec_trx_id(rec, index, *offsets)));

  rw_lock_s_lock(&(purge_sys->latch));
  version = rec;

  for (;;)
  {
    mem_heap_t *heap2 = heap;
    heap = mem_heap_create(1024);

    err = trx_undo_prev_version_build(rec, mtr, version, index, *offsets, heap, &prev_version);
    if (heap2)
    {
      mem_heap_free(heap2); /* free version */
    }

    if (err != DB_SUCCESS)
    {
      break;
    }

    if (prev_version == NULL)
    {
      /* It was a freshly inserted version */
      *old_vers = NULL;
      err = DB_SUCCESS;

      break;
    }

    *offsets = rec_get_offsets(prev_version, index, *offsets, ULINT_UNDEFINED, offset_heap);
    prev_trx_id = row_get_rec_trx_id(prev_version, index, *offsets);

    if (read_view_sees_trx_id(view, prev_trx_id))
    {
      /* The view already sees this version: we can copy
      it to in_heap and return */

      buf = mem_heap_alloc(in_heap, rec_offs_size(*offsets));
      *old_vers = rec_copy(buf, prev_version, *offsets);
      rec_offs_make_valid(*old_vers, index, *offsets);
      err = DB_SUCCESS;

      break;
    }

    version = prev_version;
  } /* for (;;) */

  mem_heap_free(heap);
  rw_lock_s_unlock(&(purge_sys->latch));

  return (err);
}
